Electroluminescent device and display pixel structure using the same
a technology of electroluminescent devices and pixel structures, applied in electrical devices, semiconductor devices, organic semiconductor devices, etc., can solve the problems of poor light extraction efficiency of current amoleds, unsatisfactory energy efficiency of oled displays, and inapplicability to light extraction of oled displays, etc., to achieve excellent light extraction efficiency, high light extraction efficiency, and excellent viewing characteristics
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embodiment 1
vice Configurations
[0082]FIG. 1(a) depicts the AMOLED pixel structure 1 with a flat bottom reflective electrode (Ag) and the surrounding dielectric bank. FIG. 1(b) depicts the proposed 3D AMOLED pixel configuration 3 with the selective high-index filler and the bottom reflective electrode (Ag) being extended to the bank slope to form the concave reflector. Different light ray paths illustrate how light rays entering the filler with an initial internal angle θint exceeding θc (the total-internal-reflection-TIR critical angle of the filler-air interface) can be re-directed for out-coupling via one or multiple reflection by various reflective surfaces. This structure is called the R-bank+filler structure 3, in which an additional dielectric layer coated over the bank slope portion of the bottom reflective electrode may be needed for insulation and for defining the emission aperture at the bottom surface. FIG. 1(c) depicts the AMOLED pixel structure along with the addition of the high-i...
embodiment 2
Structure Parameters
[0098]FIG. 4(a)-4(d) depict influences of structures on out-coupling efficiency in the R-bank+filler structure. FIG. 4 (a) is calculated ηext as a function of the bank angle θB for thin Ag devices 1-2 and ITO device 3, with W1=13 μm, H=2 μm. FIG. 4(b) is calculated ηext as a function of the bank height H for thin Ag devices 1-2 and ITO device 3, with W1=13 μm, θB=30°. FIG. 4(c) is calculated ηext as a function of the bottom width W1 for thin Ag devices 1-2 and ITO device 3, with H=2 μm, θB=30°. Assume isotropic green emitters in all devices. FIG. 4(d) is calculated ηext as a function of the bank height H for ITO devices 3 having different W1 of 26, 13, 6.5, 3.25 μm, and θB=30°. The inset of FIG. 4(d) depicts ηext as a function of H / W1 for devices 3 of different W1, to show that ηext is universally governed by the H / W1 aspect ratio, not the absolute H value.
[0099]Different pixel structure parameters influence on light extraction ηext, such as the bank angle θB, th...
embodiment 3
ctive Index of the Filler Material
[0100]Varied refractive indexes of the filler material influence on light extraction ηext. FIG. 5 shows ηext for devices 3 (ITO device) in the R-bank+filler structure as a function of the refractive index nfiller of the filler layer for isotropic green emitter, HR=67%, W1=13 μm, H=2 μm, θB=30° case. It is seen that ηext achieves optimal values around nfiller≥refractive indexes of OLED active layers (n), and drops evidently as nfiller decreases below refractive indexes of OLED active layers (assuming n˜1.8). This is mainly because the optical coupling efficiency ηfiller from the OLED emitting layers to the filler layer drops as nfiller decreases below refractive indexes of OLED emitting layers. Thus to achieve optimal possible ηext, it is preferred to keep nfiller≥(refractive indexes of OLED active layers)−0.2. In the preferred embodiment, the refractive index nfiller of the filler layer is from 1.82 to 1.88.
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Abstract
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